The present invention relates to transmission chains, particularly roller chains adapted to be used on cycles or for other applications.
Chains of this type comprise alternate inner and outer links which are articulated to one another, each link being composed of two parallel plates. In a first type of chain (GB-A No. 830 700) the plates of the inner links are connected together by bushes in which turn solid or hollow pins fixed between the two plates constituting the outer links. In another type of chain (FR-A No. 2428769) the plates constituting the inner links are provided on their opposite faces with tubular studs or barrels in which pass the pivot pins connecting these inner links and the outer links. The plates constituting the outer links may also be provided with tubular studs on their opposite faces. These two types of chain are generally completed by rollers disposed, as the case may be, around the bushes connecting the inner plates or around the hollow studs of these same plates of the inner links.
In the different chains already known the width of the chain or its lateral dimension, in a direction perpendicular to its axis or, in other words, in a direction parallel to the pivot pins between the links, is determined in the following manner: the distance between the two opposite faces of the plates forming the inner links must be at least equal to the thickness of the teeth which are to engage between these two plates. To this basic distance are added:
the functional clearances between the inner faces of the inner plates and these teeth,
the thickness of the two plates constituting an inner link;
the functional clearances between the plates of the inner links and the plates of the outer links and also, in certain cases, the projection of the bushes extending between the two plates of the inner link and possibly projecting from the outer faces of these plates;
the thickness of the two plates constituting the outer link;
where applicable, any projection of the pivot pins or outward offset of the outer plates in the zone of the pivot pins.
However this may be, in all existing chains the distance separating the plates constituting an inner link, whether in the central zone of these plates or in their end zones where the pins are situated, is always greater than the thickness of the teeth of the sprockets with which the chain has to cooperate, this thickness being measured at the roots of the teeth of these sprockets.
The result is that the thickness of chains in the direction of the pivot pins between the links cannot be less than a certain value, and this, particularly in their application to derailleur transmissions for cycles, has the consequence of limiting the number of sprockets which the freewheel may comprise, and consequently the number of gear ratios of the cycle thus equipped.
The present invention seeks to provide a chain which, while permitting operation with sprockets having a determined tooth thickness, have smaller dimensions and in particular snaller transverse width than known chains.
It therefore has as its object a transmission chain of the type comprising inner links consisting of two inner plates disposed parallel, outer links articulated on the inner links and consisting of two outer plates likewise disposed parallel, the inner plates and the outer plates comprising a central zone and two end zones where the pivot pins are disposed, the inner plates being deformed in their end zones on both their faces and delimiting projecting portions directed towards the interior of the chain, this chain being characterized in that said projecting portions are separated by a distance less than the minimum distance between the central zones of the inner plates and less than the thickness of the roots of the sprocket teeth with which the chain has to cooperate.
According to other characteristics:
the chain being of the type comprising rollers disposed around each articulation between inner links and outer links, the inwardly projecting portions extend over a zone whose diameter corresponds approximately to that of the rollers;
said projecting portions delimit, in the zone adjoining the central zone, a portion of surface adjacent the periphery of the rollers and adapted to serve as support surface for the teeth of the sprockets,
the inner plates have an undercut along the inner edges of their end zones or portions;
this undercut is in the form of a bevel preferably extending between two approximately concentric arcs of circles having, in the one case, a radius smaller than that of the roller and, in the other case, a radius greater than that of this roller;
the rollers have a thickness substantially smaller than the space between the central zones or portions of the inner plates.